1. Field of the Invention
The present invention relates to the display of digital data. More particularly, the present invention relates to high resolution, multiple color display of bit mapped images.
2. Description of the Prior Art
Prior art scanning displays have a light gun of a single color that moves an electron beam along a line from left to right on a display screen having about 480 lines from top to bottom. Display information is represented on the screen by turning the electron beam "on" and "off" as it is moved across each line. A corresponding digital memory, within an associated computer referred to as the frame buffer memory, includes a matrix of data storage locations (bits), each of which represents the "on" or "off" condition of the electron beam at some point on the display screen.
The number of bits in memory equals the number of individual, separately addressable locations on the display screen. The number of discrete screen locations determines display resolution. To achieve a display resolution of 640 locations per line in a display having 480 lines (referred to as a "high resolution" display of 640.times.480), a digital memory of 307,200 bits is required to store an image to be displayed.
The image information stored in memory provides a continuously read electronic map of the display screen surface that continuously effects the control of the electron beam as it is moved across the display screen. Such technique is referred to as bit mapping--i.e. each bit in memory has a one-to-one (mapped) relationship with a corresponding screen location. The "on" or "off" condition of the bit at each memory location mandates the "on" or "off" condition of the electron beam at that point on the display screen. High resolution is achieved by increasing the number of display locations and the corresponding number of memory bits.
A color display requires the addition of color information for each screen location (or memory bit) as well as beam "on" and "off" information. If, for example, one of four colors is be displayed per screen location, then two bits are required per location to store the one-of-four color selection information. For a four color, 640.times.480 resolution screen, 640.times.480.times.2 or 614,400 memory bits are required. If 16 colors are to be provided per screen location, then 680.times.480.times.4 or 1,228,800 memory bits are required.
As resolution or color choice increases, memory size must also increase. The industry standard establishes a display of 640.times.480 as a high resolution display, a display of 768.times.768 as a very high resolution display, and a display of 1,024.times.1,024 as an ultra high resolution display. High color selection is considered to be one having a choice of 64 colors. Accordingly, for an ultra high resolution, 64 color system, a memory of 1,024.times.1,024.times.6 or 6,291,456 bits of memory are required.